Hot melt adhesives, 100% solids materials, which are applied to a substrate when molten and cooled to harden the adhesive layer, are widely used for industrial applications.
Most commercially available hot melt adhesives require temperatures of 350.degree. F. or greater to ensure complete melting of all the components and also to achieve a satisfactory application viscosity. The need for such elevated temperatures is not without problems. The high temperatures increase the operators risks with respect both to burns and to inhalation of residual volatiles. In addition, the high temperatures require more energy, placing greater demands on the manufacturing facility.
Adhesive formulations, which can be applied at temperatures below 300.degree. F., can be prepared using low molecular weight components or a high wax content. Although these formulations achieve a low application viscosity, there is a resulting loss of adhesive properties. Therefore to improve adhesion, softer or more amorphous components are added. However, these amorphous components reduce the effective heat resistance, particularly under cantilever stressed bonds subjected to high temperatures for an extended duration.
Accordingly it would be desirable to have an adhesive which has good bond strength with exceptional heat resistance and application viscosity, even if prepared with low molecular weight components for application at low temperatures.
The adhesive compositions of the present invention can be applied at lower temperatures of 200 to 300.degree. F. yet still provide exceptional heat resistance despite using low molecular weight components which would conventionally be thought to produce poor heat and cold resistance.
Accordingly, the adhesives of the present invention find use in case sealing operations. Corrugated cases are often subjected to high stresses and adverse environmental conditions during shipping. The adhesives of the present invention meet the rigorous requirements for this and other applications.